1. Field of the Invention
The present invention relates to a hub unit on which a wheel assembly is mounted.
2. Description of Related Art
A hub unit, for example, is used as a member that supports a wheel assembly of a vehicle rotatably with respect to a suspension. This hub unit includes a rolling bearing and a cylindrical hub wheel (see, for example, Japanese Patent Application Publication No. 2007-1341 A (JP2007-1341 A) (FIGS. 1 and 5)). The hub wheel serves as a bearing ring member of the rolling bearing. The hub unit (a bearing apparatus for a wheel assembly) described in JP2007-1341 A is configured such that an annular flange portion (a wheel assembly attachment flange) extending outwardly in a radial direction is provided integrally with an end portion of the hub wheel (a hub ring) at a vehicle outer side. A hub bolt for attaching a wheel of a wheel assembly and a brake disc is fixed to the flange portion.
Further, a pilot portion extending toward the vehicle outer side is provided integrally with the end portion of the hub wheel at the vehicle outer side so as to guide attachment of the wheel of the wheel assembly and the like. A nut screwed to a drive shaft pressed into an inner periphery of the hub wheel is inserted into this pilot portion. Further, a cap that covers an opening at the vehicle outer side is attached to the pilot portion so as to prevent occurrence of rust on an inner periphery of the pilot portion. A lug portion is formed on an outer periphery of a leading end portion of this cap. When this lug portion is engaged with an annular groove formed on the inner periphery of the pilot portion, it is possible to reliably fix the cap to the pilot portion.
In order to replace the hub unit, it is necessary to remove the cap from the pilot portion of the hub wheel and remove the nut screwed to the drive shaft. However, since the cap is fixed by engaging the lug portion with the annular groove of the pilot portion, it is difficult to remove the cap from the pilot portion. This causes such a problem that an operation of replacing the hub unit cannot be performed efficiently.